This program does not yet work as intended.

This "Hello, world!" program is intended to provide an example of how
a normal app developer can deal with the Sugar desktop. Example usage
of every Sugar API is the goal, without being tied to a specific
toolkit. The program is thus plain C with a plain Makefile, using
only the bare minimum libraries.

Existing documentation is sparse and misleading, to put it mildly.
What little exists is here:

http://wiki.laptop.org/go/Activity_DBus_API
http://wiki.laptop.org/go/Activity_Protocol
http://wiki.laptop.org/go/Activity_bundles
http://wiki.laptop.org/go/Making_SVG_Icons_for_Sugar
http://wiki.laptop.org/go/Presence_Service_DBus_API
http://wiki.laptop.org/go/Shared_Sugar_Activities
http://wiki.laptop.org/go/Sugar_Icon_Format

Good luck.
